Mirrors and Lenses
IMAGES IN A PLANAR MIRROR
• Images are formed behind the mirror!!!!!
• These images are upright and are called virtual images
• Real images are formed upside down!! (More on this later)
• Distance of the object is equal to the distance of the image
formed!!!
RELATIONSHIP
• The relationship of the object distance, image
distance and focus are related
• 1 +1 =1
(Leave d in cm)
di do ƒ
–ƒ is positive for convex lenses
–do is always positive
–di is positive for real images
Sample problem: Find the focal length if
do= 5 cm and di = 20 cm.
• Convex lenses are converging lenses
–They bring light together
CONCAVE AND CONVEX MIRRORS
LENSES TERMS
Focal Point or Focus
Optical Axis
DRAWING RAYS
• Rays parallel to the Optical Axis will refract
through the Focus on the far side
• The yellow arrow represents the object.
DRAWING RAYS
• Rays directed through the near focus refract
parallel
DRAWING RAYS
Rays directed through the center of the lens
are unchanged
Drawing ray diagrams
• The red arrow represents the image. (It is drawn
from the optical axis to the point where the rays
meet)
do
di
REAL IMAGES
• Real images are formed when light converges
• Rules for Real images
– Always inverted
– Can be projected on a screen
– Appear on the other side of the lens
VIRTUAL IMAGES
• Virtual images are formed by refracted light that diverges
• Rules for Virtual Images
– Always upright
– Cannot be projected on a screen
– Appear on the same side of the lens